This invention relates to photographic processing apparatus and more particularly, it concerns an improved apparatus for delineating opposite marginal edges of a processing fluid layer as it is spread between negative and positive sheets over the image format area of self-processing, large format cameras.
As described in a commonly assigned U.S. Pat. No. 4,054,231, entitled "Photographic Apparatus" and issued Oct. 18, 1977 to Vaito K. Eloranta, technology is available for in-camera exposure and processing of photographic sheet material having image format areas of several square feet. Cameras employing this technology have been constructed and in use have demonstrated a capability for producing photographic prints of exceptionally high quality in formats as large as 40" by 84". While extremely large format cameras of this type are in the nature of a laboratory room which can be entered by an adult person and operated from within to photograph subjects positioned in the optical field of the camera, formats on the order of 20" by 24" can be accomodated by cameras adequately mobile to be transported and positioned in relation to stationary subjects.
The construction of such large format cameras conventionally entails the provision of a lens and shutter supported by a movable lens board defining a light-tight enclosure with a bellows and camera body. Associated with the camera body is a hinged back capable of supporting separate rolls of negative and positive photographic sheet material used in diffusion transfer photographic processing. As is well known in the art, such processing involves the exposure of negative sheet material and the distribution of a processing fluid between the exposed negative and a superimposed positive sheet to which the latent negative image is transferred as a positive photographic print. As disclosed in the afore-mentioned patent, the negative sheet material in large format cameras of the general type under discussion is preferably fed downwardly in the camera film plane from a roll located near the top of the camera body interior. After exposure, the negative is superimposed with a sheet of positive material fed from a roll located near the bottom of the camera body interior. The superimposed sheets are drawn between the nip of a motor driven processing roller pair so that processing fluid deposited on the sheets in accordance with the disclosure of the afore-mentioned patent is spread fully and uniformly over the image format area. As the two sheets and processing fluid are fed through the processing roller pair, they emerge from the bottom of the camera body and after a suitable imbibition time, are separated to provide the finished positive and the spent negative sheet to be discarded.
Complete coverage of the image format area by the processing fluid is assured by depositing a metered quantity of the fluid in advance of the bottom margin of the exposed negative area so that as the negative and positive sheets pass the nip of the pressure roll pair, the supply of fluid will be exhausted only after the top margin of the exposed area has passed the nip. Because the side edges of both sheets at the region in advance of the roll nip are opened or spaced, some provision must be made to contain the fluid laterally and thus delineate side margins of the applied processing fluid at or slightly outside of the opposite side margins of the image format area.
The problem of laterally containing a puddle or pool of fluid above the nip of a roller pair through which a pair of sheets are fed to sandwich the fluid, in itself, is not unique to handling processing fluid in large format cameras of the type mentioned. In the manufacture of certain types of multi-layer film packs, for example, a fluid to be spread uniformly between two superimposed sheets is fed continuously through an appropriate supply nozzle to a region overlying the nip of a pair of rollers about each of which one of the two sheets is trained. Lateral containment of the fluid thus applied has been accomplished by an organization of a downwardly and inwardly directed air jet defining ends of a puddle maintained to a pre-determined height above the nip by suction means to prevent the quantity of the liquid puddle from exceeding the capacity of the air jet. While this solution to lateral containment of a continuously supplied fluid to continuously fed sheets has been used effectively in processing manufacture of photographic materials, the apparatus employed does not account in any way for the space constraints of a camera environment and particularly, the need for presenting the unobstructed image format area of a negative sheet for exposure to be followed immediately by the application of processing fluid.